In general, in a manufacturing process of a semiconductor device, a fine pattern is formed using photolithography. Further, the fine pattern is typically formed using a plurality of transfer masks that are called photomasks. This transfer mask is generally a transparent glass substrate having a fine pattern, which is formed of a metal thin film or the like, formed on a main surface thereof. Also in manufacturing the transfer masks, photolithography is used.
In manufacturing a transfer mask using photolithography, a mask blank having a thin film (for example, a light-shielding film) for forming a transfer pattern (mask patter) on a transparent substrate such as a glass substrate is used. The manufacturing of a transfer mask using a mask blank has a drawing step of drawing a desired pattern on a resist film formed on the mask blank, a developing step of developing, after the drawing, the resist film to form a desired resist pattern, an etching step for forming the thin film with the resist pattern being used as a mask, and a step of separating and removing a remaining resist pattern. In the developing step, after the desired pattern is drawn on the resist film formed on the mask blank, a developer is supplied to dissolve a portion of the resist film soluble in the developer, thereby forming the resist pattern. Further, in the etching step, an exposed portion of the thin film on which no resist pattern is formed is removed by dry etching or wet etching with the resist pattern being used as a mask, thereby forming the desired mask pattern on the transparent substrate. In this way, the transfer mask may be manufactured.
As kinds of the transfer mask, other than a related-art binary type mask having a light-shielding film pattern formed of a chromium-based material on a transparent substrate, a phase shift type mask (also simply referred to as “phase shift mask”) is known. The phase shift type mask has a structure including a phase shift film on a transparent substrate. The phase shift film causes a predetermined phase difference with respect to exposure light, and, for example, a material containing a molybdenum silicide compound is used. Further, a binary type mask in which a material containing a silicide compound of a metal such as molybdenum is used as a light-shielding film is also coming into general use. These binary type masks and phase shift type masks are herein collectively referred to as transmission type masks. Further, binary type mask blanks and phase shift type mask blanks serving as originals used for transmission type masks are collectively referred to as transmission type mask blanks.
As described above, increasing demand for forming finer patterns in a lithography step causes problems in the lithography step to be noticeable. One of the problems relates to defect information on a mask blank substrate used in the lithography step.
As the mask blank substrate, from the viewpoint of improvement in defect quality accompanying finer patterns in recent years and of optical characteristics required for the transfer mask, a smoother substrate is required.
As a typical method of manufacturing precision polished glass, for example, there is described in JP-A-S64-40267 (Patent Document 1) a method of manufacturing precision polished glass in which, after a glass surface is polished using a polishing material with cerium oxide being a main material thereof, polish finishing is given using colloidal silica.
A mask blank to be an original of a transfer mask used in photolithography is produced by forming, on a substrate of synthetic quartz glass or the like, a thin film for pattern formation by sputtering. A substrate used for a mask blank is required to have no defect on a main surface thereof, or, if there are some, the number of the defects is required to be a predetermined number or less. Therefore, defect inspection is generally made to the main surface of the substrate using a defect inspection apparatus as disclosed in JP-A-2001-027611 (Patent Document 2) and JP-A-2002-328099 (Patent Document 3), thereby inspecting whether or not there is a defect on the main surface or the like.